[SCM] GNU Autoconf source repository branch, master, updated. v2.65-100-g60e32aa

[Eric Blake]

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- Log -----------------------------------------------------------------
commit 60e32aa3fc8a7c9c312aa6aed3187e4e943b559e
Author: Bruno Haible <address@hidden>
Date:   Sat Jun 19 00:49:48 2010 +0200

    Document how to use literal newlines in makefile rules.
    
    * doc/autoconf.texi (Newlines in Make Rules): New section.
    
    Signed-off-by: Eric Blake <address@hidden>

commit 85b2b2056e4f77313bad613d7bf18ab63f942606
Author: Bruno Haible <address@hidden>
Date:   Sat Jun 19 00:06:37 2010 +0200

    Document how to write comments in makefile rules.
    
    * doc/autoconf.texi (Comments in Make Rules): Mention a workaround
    syntax.
    
    Signed-off-by: Eric Blake <address@hidden>

commit eb1ca4966a0046d9efd9d0935e58dd8469f1cef6
Author: Ben Pfaff <address@hidden>
Date:   Mon Jun 14 21:10:48 2010 -0700

    Document how to propogate variables to submakes.
    
    On bug-gnulib, archived at
         http://permalink.gmane.org/gmane.comp.lib.gnulib.bugs/22132
    Ralf Wildenhues taught me a bit about how Automake propagates
    variables to submakes.  I thought that it would good to document
    this in the Autoconf manual, which currently has no detail at
    all.
    
    * doc/autoconf.texi: Describe technique used by Automake to
    propagate variables to submakes in more detail.
    
    Signed-off-by: Eric Blake <address@hidden>

commit bea3f1684a2773ef711dc46ec341f4b8aef153c9
Author: Peter Johansson <address@hidden>
Date:   Tue Jun 22 21:09:04 2010 -0400

    Be consistent in doc example.
    
    * doc/autoconf.texi: (Polymorphic Variables) be consistent in code
    example and output
    
    Signed-off-by: Eric Blake <address@hidden>

-----------------------------------------------------------------------

Summary of changes:
 ChangeLog         |   21 ++++++++++++++++
 doc/autoconf.texi |   67 ++++++++++++++++++++++++++++++++++++++++++++++------
 2 files changed, 80 insertions(+), 8 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index d59487e..024a835 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,24 @@
+2010-06-22  Bruno Haible  <address@hidden>
+
+       Document how to use literal newlines in makefile rules.
+       * doc/autoconf.texi (Newlines in Make Rules): New section.
+
+       Document how to write comments in makefile rules.
+       * doc/autoconf.texi (Comments in Make Rules): Mention a workaround
+       syntax.
+
+2010-06-22  Ben Pfaff  <address@hidden>
+
+       Document how to propogate variables to submakes.
+       * doc/autoconf.texi: Describe technique used by Automake to
+       propagate variables to submakes in more detail.
+
+2010-06-22  Peter Johansson  <address@hidden>  (tiny change)
+
+       Be consistent in doc example.
+       * doc/autoconf.texi: (Polymorphic Variables) be consistent in code
+       example and output
+
 2010-06-22  Ralf Wildenhues  <address@hidden>
 
        Add comments for vim syntax highlighting.
diff --git a/doc/autoconf.texi b/doc/autoconf.texi
index 77013d4..1060955 100644
--- a/doc/autoconf.texi
+++ b/doc/autoconf.texi
@@ -529,6 +529,7 @@ Portable Make Programming
 * The Make Macro SHELL::        @code{$(SHELL)} portability issues
 * Parallel Make::               Parallel @command{make} quirks
 * Comments in Make Rules::      Other problems with Make comments
+* Newlines in Make Rules::      Using literal newlines in rules
 * obj/ and Make::               Don't name a subdirectory @file{obj}
 * make -k Status::              Exit status of @samp{make -k}
 * VPATH and Make::              @code{VPATH} woes
@@ -13415,7 +13416,7 @@ can handle composed shell variable names:
 @example
 m4_define([MY_CHECK_HEADER],
 [AS_VAR_PUSHDEF([my_Header], [ac_cv_header_$1])dnl
-AS_VAR_IF([my_Header], [yes], [echo "header $1 available"])dnl
+AS_VAR_IF([my_Header], [yes], [echo "header $1 detected"])dnl
 AS_VAR_POPDEF([my_Header])dnl
 ])
 MY_CHECK_HEADER([stdint.h])
@@ -18561,6 +18562,7 @@ itself.
 * The Make Macro SHELL::        @code{$(SHELL)} portability issues
 * Parallel Make::               Parallel @command{make} quirks
 * Comments in Make Rules::      Other problems with Make comments
+* Newlines in Make Rules::      Using literal newlines in rules
 * obj/ and Make::               Don't name a subdirectory @file{obj}
 * make -k Status::              Exit status of @samp{make -k}
 * VPATH and Make::              @code{VPATH} woes
@@ -18753,8 +18755,8 @@ environment contains some other macros usually defined 
by the
 makefile.  (See also the note about @code{make -e} and @code{SHELL}
 below.)
 
-Another way to propagate overrides to submakes is to do it
-manually, from your makefile:
+If you can foresee all macros that a user might want to override, then
+you can propagate them to submakes manually, from your makefile:
 
 @example
 foo = foo
@@ -18765,12 +18767,25 @@ two:
         @@echo $(foo)
 @end example
 
-You need to foresee all macros that a user might want to override if
-you do that.
+Another way to propagate a variable to submakes in a portable way is to
+expand an extra variable in every invocation of @samp{$(MAKE)} within
+your makefile:
 
-Makefiles generated by @command{automake} expand @code{$(AM_MAKEFLAGS)}
-on the command line of submakes, which can be used for propagated overrides
-(@pxref{Subdirectories, , Automake, automake, GNU Automake}).
address@hidden
+foo = foo
+one:
+        @@echo $(foo)
+        $(MAKE) $(SUBMAKEFLAGS) two
+two:
+        @@echo $(foo)
address@hidden example
+
+Users must be aware that this technique is in use to take advantage of
+it, e.g.@: with @code{make foo=bar SUBMAKEFLAGS='foo=bar'}, but it
+allows any macro to be overridden.  Makefiles generated by
address@hidden use this technique, expanding @code{$(AM_MAKEFLAGS)}
+on the command lines of submakes (@pxref{Subdirectories, , Automake,
+automake, GNU Automake}).
 
 @node The Make Macro MAKEFLAGS
 @section The Make Macro MAKEFLAGS
@@ -18952,6 +18967,42 @@ all:
         # foo
 @end example
 
+As a workaround, you can use the @command{:} no-op command with a string
+argument that gets ignored:
+
address@hidden
+all:
+        : "foo"
address@hidden example
+
address@hidden Newlines in Make Rules
address@hidden Newlines in Make Rules
address@hidden Newlines in @file{Makefile} rules
address@hidden @file{Makefile} rules and newlines
+
+In shell scripts, newlines can be used inside string literals.  But in
+the shell statements of @file{Makefile} rules, this is not possible:
+A newline not preceded by a backslash is a separator between shell
+statements.  Whereas a newline that is preceded by a backslash becomes
+part of the shell statement according to POSIX, but gets replaced,
+together with the backslash that precedes it, by a space in GNU
address@hidden 3.80 and older.  So, how can a newline be used in a string
+literal?
+
+The trick is to set up a shell variable that contains a newline:
+
address@hidden
+nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"
address@hidden example
+
+For example, in order to create a multiline @samp{sed} expression that
+inserts a blank line after every line of a file, this code can be used:
+
address@hidden
+nlinit=`echo 'nl="'; echo '"'`; eval "$$nlinit"; \
+sed -e "s/\$$/address@hidden@}/" < input > output
address@hidden example
+
 @node obj/ and Make
 @section The @file{obj/} Subdirectory and Make
 @cindex @file{obj/}, subdirectory


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